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I was just reading some of the coverage of Yellowstone’s recent earthquake swarm.

Let me get you up to speed in case you haven’t been following this. There has been an increase in mild earthquake activity in Yellowstone Park recently. Mild earthquakes are common there because Yellowstone Park sits on top of an active volcano. We say that the volcano is active because there is magma five miles underground, not because it is erupting or necessarily about to erupt.

Before you freak out, scientists say an eruption is not imminent. You can check some of the links near the bottom of New West Blog‘s post if you need to relax.

The University of Utah is tracking the earthquakes. Most of the earthquakes have been below 2.0 on the Richter scale. The biggest was had a magnitude of 3.5. (You can see this in the MAG column on the left.) Depth is worth looking at even though many regular news reports ignore depth. Depth is important because it affects how strongly the earthquake is felt at the surface. The magnitude only tells you how strong the earthquake was underground where it actually happened. We care more about what happens up here on the surface so we have to pay attention to magnitude and depth. Until January 3, most of the earthquakes were really shallow, just a few kilometers deep.

Let’s compare that to a worldwide list of earthquakes published by the U.S. Geological Survey. This chart includes earthquakes worldwide with a magnitude greater than 2.5, so some of the Yellowstone quakes aren’t included. Scroll down to January 3 and 4, 2009. (Look here if you read this between Jan 10 and Feb 3, 2009. After that, I think you’re out of luck.) There were more medium and large earthquakes near the north coast of Paupa, Indonesia than at Yellowstone. Also notice that the Indonesian quakes were much deeper.

Why do Wyoming and Indonesia have such different earthquakes? It’s because of the structure of the earth in those regions.

I want to remind you of 9th grade for a minute. Don’t worry. You don’t have to have get pimples or listen to Ratt. You only need to remember one thing from earth science. The surface of the earth (including the ocean floor) is made up of around a dozen plates that move around very slowly.

Alright, back to 2009, male pattern baldness, and roof raking.

Indonesia is right over an area where two plates are colliding. One plate is actually being forced under the other one. An area where this happens is called a subduction zone. Subduction is what is causing those deep earthquakes.

This is happening all around the Pacific Rim, from Chile, up past Mexico to California, around Alaska to Russia, then south past Japan to Indonesia and on to New Zealand. People call this huge chain of subduction zones the Ring of Fire. (Think for a second, if the edges of the Pacific Ocean are being forced under continents, is the Pacific Ocean getting bigger or smaller?)

Geologists say that Yellowstone Park is over a hot spot. That’s because there was a big convention there in 1953 and everybody got wasted and went cow tipping. No, actually a hot spot is an area in the middle of a plate that still has a lot of volcanic activity. Wyoming, where Yellowstone is located, is in the middle of the North American plate, so it’s impossible for another plate to slip under it.

It’s pretty easy to imagine why there would be volcanoes and earthquakes in subduction zones. It’s harder to understand why hot spots occur. I can’t explain it to you today.

Please remember what they said and don’t freak out. It doesn’t look like there will be any sort of eruption soon in Yellowstone National Park.Not happening soon